(1) Field of the Invention
This invention relates to respiratory humidifiers and heated breathing conduits used to couple a patient to the humidifier. A fault protection system for the conduit heater wire is disclosed.
(2) Description of the Prior Art
In order to supply gases to a patient or a person needing such gases, it may sometimes be necessary to first humidify those gases, for example using a respiratory humidifier/ventilator system. In such a case where the gases have been humidified, and therefore laden with water, it is likely that during transport through a conduit to the patient, condensation of that water vapour will occur. In order to overcome this disadvantage it is known to associate a heater wire with respiratory humidifier breathing conduits to avoid condensation. Examples of such a heated breathing conduit are disclosed in U.S. Pat. No. 5,537,996 (McPhee) and U.S. Pat. No. 5,392,770 (Clawson et al.).
However there are safety concerns with using a heated wire system, especially when the gas in the breathing conduit contains a high concentration of oxygen, which may be a common condition in hospitals. It is possible for ignition of the heater wire and conduit materials to occur if certain fault conditions are present. Thus physicians may be hesitant to use a humidifier with an associated heater wire, due to the perceived risks to the patient. However if the a humidifier is not used various respiratory problems can occur due to the lack of controlled humidity.
It is an object of the present invention to provide a fault protection system for a respiratory conduit heater element which goes some way towards overcoming the abovementioned disadvantages.
Accordingly, in a first aspect, the present invention consists in a fault protection system for a respiratory conduit heater element comprising:
detecting means which include means to detect a rapid change of current in said heater element,
current interruptor means in series with said heater element, and
timer means adapted to control the action of said interruptor means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means.
In a second aspect, the present invention consists in a semiconductor switching circuit for rapidly controlling the AC supply current through a load from a power supply comprising:
two same channel MOSFETs connected in series with their source and gate electrodes respectively tied together, said circuit adapted to receive a switching voltage between the commoned gate and source electrodes, their drain electrodes adapted to be connected to a load and a power supply respectively.
In a third aspect, the present invention consists in a semiconductor switching circuit for rapidly controlling the AC supply current through a load from a power supply comprising:
two same channel MOSFETs connected in series with their drain and gate electrodes respectively tied together, said circuit adapted to receive a switching voltage between the commoned gate and drain electrodes, their source electrodes adapted to be connected to a load and a power supply respectively.
In a fourth aspect, the present invention consists in a fault protection system for a respiratory conduit heater element comprising:
a detector means which includes a peak current detector for detecting current in the heater element
a current interruptor in series with said heater element, and
a timing circuit adapted to control the action of said current interruptor and thereby in use determining the duration of current interruption, said timing circuit being triggered by said detector, when a predetermined threshold current is exceeded.
In a fifth aspect, the present invention consists in a respiratory humidification system wherein a conduit connects a patient to a humidifier, said conduit being heated by a respiratory conduit heater element controlled by said humidifier, the improvement comprising that said humidifier includes a fault protection system for said heater element comprising:
detecting means which include means to detect a rapid change of current in said heater element,
current interruptor means in series with said heater element, and
timer means adapted to control the action of said interruptor means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means.
In a sixth aspect, the present invention consists in a respiratory humidification system wherein a conduit connects a patient to a humidifier, said conduit being heated by a respiratory conduit heater element controlled by said humidifier, the improvement comprising that said humidifier includes a fault protection system for said heater element comprising:
detecting means which includes a peak current detector for detecting current in the heater element
current interruptol means in series with said heater element, and timer means adapted to control the action of said interruptor means and thereby in use determining the duration of current interruption, said timer means being triggered by said detecting means, when a predetermined threshold current is exceeded.